生物质与原位吸附生物油共热解过程中易结焦组分转化机理研究

The utilization of bio-oil is limited mainly due to the presence of coking components, such as polymeric or oligomeric sugars and phenols. It is reported that such coking components can be removed completely without hydrogen and catalyst in a countercurrent moving bed reactor, in which the co-pyrolysis of biomass and in-situ adsorbed bio-oil is maximized. However, the conversion mechanism of the coking components during the co-pyrolysis and its applicability to other pyrolysis systems are unclear and need to be further studied. In this project, a preliminary conversion mechanism will be proposed by the studies on co-pyrolysis of bio-oil and char models, which are selected based on comprehensive analyses of bio-oil by gas chromatography-mass spectrometry (GC-MS), two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOF), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and characterization of char with in-situ infrared spectrometry (In-situ IR). A simplified co-pyrolysis process, which avoids the influence of self-pyrolysis of biomass, is designed by employing bio-oil and tar-free chars from different temperatures and investigated with a thimble wire-mesh multi-stage reactor to further improve the proposed mechanism. Finally, both yield and quality of bio-oil from oil-rich pyrolysis systems (e.g. fluidized bed pyrolysis unit) will be optimized by intensifying the co-pyrolysis of biomass and adsorbed bio-oil on a basis of understanding the conversion mechanism. The study will provide scientific and technical supports for the development of novel biomass pyrolysis technologies.

生物油的提质及应用受其中多聚糖、低聚糖及酚类等易结焦组分的限制。研究发现使用逆流移动床强化热解中生物质与原位吸附生物油共热解行为，可在无外加催化剂及氢气条件下完全脱除生物油中易结焦组分。但该过程中易结焦组分转化机理及其在其它热解体系中的集成仍有待研究。本项目将使用GC-MS、GC×GC-TOF和FT-ICR MS等多种分析技术对生物油进行全组分分析，利用原位红外技术对热解过程中半焦官能团进行表征，根据分析结果选择易结焦组分及半焦模型物并展开研究，初步提出易结焦组分转化机理；然后通过合理简化生物质与原位吸附生物油共热解过程，借助套管式丝网多段反应器详细考察生物油与无挥发份半焦相互作用，对上述转化机理进行进一步验证和完善；项目最后将以易结焦组分转化机理指导富产油热解系统的优化，使生物油收率和品位同时达到最佳值。本项目的研究可促进生物质新型热解技术的开发，具有重要的理论意义和实用价值。

生物油提质及应用受其中多聚糖、低聚糖及酚类化合物等易结焦组分的限制。研究发现使用逆流移动床强化热解过程中挥发分与半焦间相互作用，可在无外加催化剂及氢气条件下完全脱除生物油中易结焦组分，但该过程中挥发分易结焦组分的脱除机制仍不明朗。本项目在掌握易结焦组分成分特征及热解过程中半焦表面活性官能团演变规律的基础上，科学地选用了易结焦组分模型化合物和半焦模型物，并详细考察不同温度下易结焦组分模型化合物与半焦模型物之间的相互作用，从反应产物的组成及分布等方面间接揭示了易结焦组分在半焦作用下的转化规律，取得了一系列重要的学术成果：1）在气相色谱-质谱可测范围内，生物油中易结焦组分成分特征受原料影响较小。无论是富含纤维素的松木还是富含木质素的棕榈仁壳，其热解挥发分中易结焦组分均以左旋葡聚糖为主；2）半焦的物理化学结构对易结焦组分转化行为影响较大。松木半焦主要使易结焦组分转化为积碳和轻油，气体产物很少，而棕榈仁壳半焦则可使易结焦组分转化为积碳、轻油和气体，并且转化为积碳和气体的程度相当；3）易结焦组分与半焦表面羟基、羧基等含氧官能团之间存在较强的相互作用，该相互作用能进一步促进易结焦组分向积碳、轻油和/或气体转化。反应温度对该相互作用影响很大。当温度低于 350 °C时，该相互作用非常微弱；但当温度高达 450 °C时，羟基官能团全部脱落，而羧基官能团仍能保持很好的反应活性；4）糠醛、甲基糠醛等呋喃类小分子是以左旋葡聚糖为代表的易结焦组分在含氧官能团作用下的主要液相产物。本项目不仅初步揭示了生物质热解挥发分与半焦相互作用时易结焦组分的转化规律，还为开发以高品位生物油为导向的生物质热解新工艺提供研究思路。